In the Fiscal sustainability report (FSR) the Office for Budget Responsibility looks beyond the medium-term forecast horizon of their twice-yearly Economic and fiscal outlooks and ask whether the UK's public finances are likely to be sustainable over the longer term. The approach is twofold: (i) Look at the fiscal impact of past government activity, as reflected in the assets and liabilities on the public sector's balance sheet; (ii) Look at the potential fiscal impact of future government activity, by making 50-year projections of all public spending, revenues and significant financial transactions, such as government loans to students. These projections suggest that the public finances are likely to come under pressure over the longer term, primarily as a result of an ageing population. Under the OBR's definition of unchanged policy, the Government would end up having to spend more as a share of national income on age-related items such as pensions and health care. But the same demographic trends would leave government revenues roughly stable as a share of national income. Long-term projections such as these are highly uncertain and the results presented here should be seen as broad-brush illustrations rather than precise forecasts. This publication is divided into 5 chapters, with two annexes and a bibliography.